Published: October 04, 2011 r2011 American Chemical Society 12741 dx.doi.org/10.1021/ie2015334 | Ind. Eng. Chem. Res. 2011, 50, 12741–12749 ARTICLE pubs.acs.org/IECR High Temperature CaO/Y 2 O 3 Carbon Dioxide Absorbent with Enhanced Stability for Sorption-Enhanced Reforming Applications V. S. Derevschikov, †,‡ A. I. Lysikov, †,‡ and A. G. Okunev †,‡, * † Novosibirsk State University, pr.Koptyuga 1, Novosibirsk 630090, Russia ‡ Boreskov Institute of Catalysis, pr.Lavrentieva 5, Novosibirsk 630090, Russia ABSTRACT: To improve the stability of high temperature CO 2 absorbent for sorption enhanced reforming applications yttria supported CaO were synthesized using two methods: calcination of mixed salt precursors and wet impregnation of yttria support. According to XRD data, CaO does not interact with the yttria matrix. However, introduction of CaO drastically changes the morphology of primary yttria particles. Increase in CaO concentration results in gradual plugging of the smaller pores and sintering of yttria support. The CO 2 absorption uptake in recarbonation-decomposition cycles increases with increase in CaO content and reach 9.6 wt % at CaO content of 19.9 wt %. CaO recarbonation extent varies from 49 to 77%. CaO/Y 2 O 3 absorbents are extremely stable under overheating and maintain their capacity in long series of decomposition-recarbonation cycles even after calcination at 1350 °C. The novel material resists moisture and retains its strength during storage in the air. According to tests, CaO/Y 2 O 3 can be considered as a promising CO 2 absorbent for fixed bed sorption enhanced hydrocarbons reforming. ’ INTRODUCTION High temperature CO 2 sorbents were successfully applied for sorption-enhanced hydrocarbons reforming process (SERP). Materials of different chemical nature: alkali promoted hydro- talcites, 1À13 lithium salts, 14À19 or calcium oxide 20À27 can rever- sibly absorb CO 2 in the temperature range of 400À900 °C, often used in catalytic steam reforming of hydrocarbons. The SERP conditions depend on the sorption properties of the particular sorbent. Isothermal sorptionÀregeneration cycles are used for promoted hydrotalcites, 1À4 for which the CO 2 desorption rate obeys a linear driving force model. 7,10 On the other hand, CaO-based sorbents are regenerated usually at elevated temperature 25,27 due to inherently slow kinetics of CaCO 3 decomposition. 28À30 Lyon and Cole presented a self- sustained thermally neutral mixed sorption-enhanced reformingÀ unmixed combustion process. 31 They used 8 atm pressure during the reforming step and an air purge at 1 atm during the regen- eration step. Even a higher pressure during the reforming step would be of interest for hydrogen production in oil refining, ammonia synthesis, or coal gasification. 32 However, at high steam and CO 2 pressures a CaO-based sorbent undergoes accelerated sintering due to formation of the eutectic mixture of CaCO 3 ÀCaOÀCa(OH) 2 . 33À35 The pro- blem can be solved through the use of supported or promoted sorbents with an active CaO component dispersed in the pores of a stable inert matrix. Examples of the promoters and supports used to date include individual or mixed oxides of magnesium, 20,26,36À46 aluminum, 46À52 lanthanum, 53,54 silicon, 55À59 titanium, 60,61 and others. 62 This paper presents the study of sorption properties of novel CaO/Y 2 O 3 sorbent. As a support, yttria has a number of attractive properties making it a very promising material in SERP. It does not react with water or CO 2 at ambient conditions, which facilitates the storage of the sorbent, does not react with either steam or carbon dioxide at elevated temperatures, and has a melting temperature of 2415 °C. Y 2 O 3 is among a few refractory oxides which do not react with CaO. The current price of yttria, while several times higher than the price of the alumina or titania, is, however, comparable to the price of a reforming catalyst and may not be prohibitive for small or middle scale reforming facilities. ’ EXPERIMENTAL SECTION Synthesis. Yttria supported CaO sorbents were prepared using two different techniques. The first method involved calcination of mixed precursors. The sorbent was synthesized as follows: 108.7 g of Y(NO 3 ) 3 3 6H 2 O (Reahim) and 33.5 g of Ca(NO 3 ) 3 3 4H 2 O (Laverna) were added to a 150 mL beaker containing 100 mL of distilled water and dissolved under vigorous stirring. The target Ca/Y atomic ratio in solution was 2. The solution was dried in an oven at 200 °C for 4 h, then the solids were slowly heated to 1300 °C in air and kept at this temperature for 2 h. The product was ground in a mortar and sieved to produce the fraction of 0.5À1 mm used in the experiments. This sorbent will be further referred to as CaY-calc. The second method uses the impregnation of yttria matrix with calcium nitrate solution. The matrix was synthesized as follows: 140 g of Y(NO 3 ) 3 3 6H 2 O were added to a 150 mL beaker containing 100 mL of distilled water and dissolved under vigorous stirring. The dried mixture was then calcined using the same calcination procedure as that described previously. The product was ground in a mortar and sieved to produce yttria grains of 1À2 mm size. The impregnation solution was prepared as follows. Ca(NO 3 ) 3 3 4H 2 O and distilled water were used to Received: July 15, 2011 Accepted: October 4, 2011 Revised: October 3, 2011